Method and apparatus for making an absorbent structure comprising channels

ABSTRACT

The present invention relates to an apparatus and method for making an absorbent structure for an absorbent article, comprising a supporting sheet and thereon an absorbent layer, the absorbent layer comprising an absorbent material. According to the present invention a first moving endless surface is provided which has one or more substantially longitudinally extending first mating strips, and at least one further auxiliary moving endless surface is provided which acts against the first mating strips. Pressure is applied between the first moving endless surface and the auxiliary moving endless surface to the first and second supporting sheets at least within a part of the area of the channels, so as to adhere together the first and second supporting sheets.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/615,467, filed on Feb. 6, 2015, which claims priority to EuropeanPatent Application Nos. EP14154594.7, filed Feb. 11, 2014, andEP15151574.9, filed Jan. 19, 2015.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for making anabsorbent structure with channels embedded within the absorbentstructure. The channels are strips that are free of absorbent material.

BACKGROUND OF THE INVENTION

Absorbent articles, such as diapers and sanitary napkins, absorb andcontain body exudates. They also are intended to prevent body exudatesfrom soiling, wetting, or otherwise contaminating clothing or otherarticles, such as bedding, that come in contact with the wearer. Adisposable absorbent article, such as a disposable diaper, may be wornfor several hours in a dry state or in a urine-loaded state.Accordingly, efforts have been made toward improving the fit and comfortof the absorbent article to the wearer, both when the article is dry andwhen the article is fully or partially loaded with liquid exudate, whilemaintaining or enhancing the absorbing and containing functions of thearticle.

Efforts have also been made to make absorbent article thinner when dry,to improve the comfort of such articles.

Some absorbent articles, like diapers, contain absorbent material suchas super absorbent polymers that absorbs very high quantities of liquidand causes the absorbent article to swell significantly. Such articleswill thus increase significantly in volume during use, and sometimes inparticular in the crotch area between the wearer's legs, which mayrender the article uncomfortable.

There is thus still a need to further improve the fit of such articlesand/or the liquid transportation away from the crotch. There is also aneed to reduce the usage of absorbent material in such articles.

There is also still a need to further reduce the chance of leakage andto improve the efficiency of absorbency of an absorbent article, such asa diaper.

It has also been found that improved liquid transportation can beachieved by the provision of transportation channels for distributingliquid in the absorbent article, e.g., the absorbent structure thereof.Furthermore, it has surprisingly been found that the amount of absorbentmaterial can be reduced hereby, whilst maintaining the performance. Ithas been found that improved fit can be obtained by providing absorbentarticles with absorbent structures whereby the absorbent material isstructured in machine direction, optionally with areas that compriseless or no absorbent material, for improved bending flexibility in use(in the direction corresponding to the machine direction).

EP-A-2 532 329, published on Dec. 12, 2012, discloses an apparatus andmethod for producing an absorbent structure comprising at least twosupporting sheets and a layer of absorbent material deposited,preferably by a printing process, onto at least one of the supportingsheets. It discloses a separate pressure roll which may selectivelyapply pressure only onto the channel area of the absorbent structure.The pressure means may comprise raised mating strips.

The present invention relates to an apparatus for making an absorbentstructure for an absorbent article, comprising a supporting sheet andthereon an absorbent layer, the absorbent layer comprising an absorbentmaterial, the apparatus comprising:

a) transfer means for transferring first and second supporting sheets tofirst and second moving endless surfaces;

b) a feeder for feeding the absorbent material onto at least the firstsupporting sheet at a depositing point on the first moving endlesssurface, the absorbent material forming absorbent regions upon thesupporting sheet, and one or more channels between the absorbentregions, the channels being substantially free of absorbent material;

c) an adhesive applicator for applying adhesive to at least one of thefirst and second supporting sheets, at least within the region of thechannels.

The present invention further relates to a method for making anabsorbent structure comprising a supporting sheet and thereon anabsorbent layer of absorbent material, the method comprising the stepsof:

a) transferring first and second supporting sheets to first and secondmoving endless surfaces;

b) feeding the absorbent material onto at least the first supportingsheet at a depositing point on the first moving endless surface, theabsorbent material forming absorbent regions and one or more channelsbetween the absorbent regions, the channels being substantially free ofabsorbent material;

c) applying adhesive to at least one of the first and second supportingsheets, at least within the region of the channels.

The present invention addresses the problem of ensuring accurateregistration between the pattern of regions free of absorbent materialformed in the depositing or printing step, and the pressure applied byseparate pressure rolls in a downstream gluing step.

The present invention combines the depositing or printing step and thepressure step which forms the channels by adhesion onto a single movingendless surface, e.g., a roll.

SUMMARY OF THE INVENTION

According to the present invention a first moving endless surface isprovided which has one or more substantially longitudinally extendingfirst mating strips, and at least one further auxiliary moving endlesssurface is provided which acts against the first mating strips. Pressureis applied between the first endless moving surface and the auxiliarymoving endless surface to the first and second supporting sheets atleast within a part of an area of the channels, so as to adhere togetherthe first and second supporting sheets.

According to a preferred embodiment of the present invention, second andthird auxiliary moving endless surfaces are provided such that the firstmoving endless surface which carries the first and second supportingsheets passes under pressure between the second and third auxiliarymoving endless surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of a reservoir 25.

FIG. 1B is a top view of an alternative reservoir 25.

FIG. 2 is a side view of an apparatus of the present invention, or usedin the method of the invention.

FIG. 3 is a partial perspective view of an apparatus of the presentinvention, or used in a method of the invention.

FIG. 4 is a partial perspective view of an alternative apparatus of thepresent invention, or used in an alternative method of the invention.

FIG. 5A is a schematic representation of a single auxiliary bondingroll.

FIG. 5B is a schematic representation of an alternative embodimentcomprising two opposing auxiliary bonding rolls.

FIG. 5C is a schematic representation of another alternative embodimentcomprising an auxiliary bonding roll and opposing support roll.

FIG. 5D is a schematic representation of another alternative embodimentcomprising an auxiliary bonding belt.

DETAILED DESCRIPTION OF THE INVENTION

As summarized above, this invention encompasses a method and apparatusfor making an absorbent structure useful for an absorbent articlecomprising absorbent material, preferably comprising at least, or only,particulate superabsorbent polymer material. Embodiments of such methodand apparatus and resulting absorbent structures and absorbent articlesare further described herein, after the following definitions.

Definitions

“Absorbent structure” refers to a three-dimension structure with alongitudinal dimension and, perpendicular thereto, a transversedimension, and, perpendicular to both, a height dimension, and thatcomprises at least an absorbent material and a supporting sheet, andthat is useful in an absorbent article.

“Absorbent layer” refers to a three dimensional layer of absorbentmaterial, formed by deposition of absorbent material onto the supportingsheet.

“Absorbent material” refers to a material or mixture of materials thatcan absorb and retain bodily fluids; it typically includes or consistsof “superabsorbent polymer material”. “Superabsorbent polymer material”(also known as “absorbent gelling material,” or “AGM,” or“superabsorbent,”) refer to polymeric material that can absorb at least10 times (and typically at least 15 times, or at least 20 times) theirweight of an aqueous 0.9% saline solution as measured using theCentrifuge Retention Capacity test (Edana 441.2-02), i.e. having a CRCof at least 10 g/g, and typically at least 15 g/g or at least 20 g/g.

“Absorbent article” refers to a device that absorbs and contains bodyexudates, and, more specifically, refers to devices that are placedagainst or in proximity to the body of the wearer to absorb and containthe various exudates discharged from the body. Absorbent articles mayinclude adult and infant diapers, including pants, such as infanttraining pants and adult incontinence undergarments, and femininehygiene products, such as sanitary napkins and panty-liners and adultincontinent pads, and breast pads, care mats, bibs, wound dressingproducts, and the like. Absorbent articles may further include floorcleaning articles, food industry articles, and the like. As used herein,the term “body fluids” or “body exudates” includes, but is not limitedto, urine, blood, vaginal discharges, breast milk, sweat and fecalmatter.

“Diaper” refers to an absorbent article generally worn by infants andincontinent persons about the lower torso so as to encircle the waistand legs of the wearer and that is specifically adapted to receive andcontain urinary and fecal waste.

“Pant” or “training pant”, as used herein, refer to diaper having awaist opening and leg openings designed for infant or adult wearers. Apant may be placed in position on the wearer by inserting the wearer'slegs into the leg openings and sliding the pant into position about awearer's lower torso. A pant may be preformed by any suitable techniqueincluding, but not limited to, joining together portions of the articleusing refastenable and/or non-refastenable bonds (e.g., seam, weld,adhesive, cohesive bond, fastener, etc.). A pant may be preformedanywhere along the circumference of the article (e.g., side fastened,front waist fastened). While the terms “pant” or “pants” are usedherein, pants are also commonly referred to as “closed diapers,”“prefastened diapers,” “pull-on diapers,” “training pants,” and“diaper-pants”. Suitable pants are disclosed in U.S. Pat. No. 5,246,433,issued to Hasse, et al. on Sep. 21, 1993; U.S. Pat. No. 5,569,234,issued to Buell et al. on Oct. 29, 1996; U.S. Pat. No. 6,120,487, issuedto Ashton on Sep. 19, 2000; U.S. Pat. No. 6,120,489, issued to Johnsonet al. on Sep. 19, 2000; U.S. Pat. No. 4,940,464, issued to Van Gompelet al. on Jul. 10, 1990; U.S. Pat. No. 5,092,861, issued to Nomura etal. on Mar. 3, 1992; U.S. Patent Publication No. 2003/0233082 A1,entitled “Highly Flexible And Low Deformation Fastening Device”, filedon Jun. 13, 2002; U.S. Pat. No. 5,897,545, issued to Kline et al. onApr. 27, 1999; U.S. Pat. No. 5,957,908, issued to Kline et al on Sep.28, 1999.

A “nonwoven” is a manufactured sheet, web or batt of directionally orrandomly orientated fibers, bonded by friction, and/or cohesion and/oradhesion, excluding paper and products which are woven, knitted, tufted,stitch-bonded incorporating binding yarns or filaments, or felted bywet-milling, whether or not additionally needled. The fibers may be ofnatural or man-made origin and may be staple or continuous filaments orbe formed in situ. Commercially available fibers have diameters rangingfrom less than about 0.001 mm to more than about 0.2 mm and they come inseveral different forms: short fibers (known as staple, or chopped),continuous single fibers (filaments or monofilaments), untwisted bundlesof continuous filaments (tow), and twisted bundles of continuousfilaments (yarn). Nonwoven fabrics can be formed by many processes suchas meltblowing, spunbonding, solvent spinning, electrospinning, andcarding. The basis weight of nonwoven fabrics is usually expressed ingrams per square meter (gsm).

“Particulate” is used herein to refer to a material which is inparticulate form so as to be flowable in the dry state.

“Substantially cellulose free” is used herein to describe an article,such as an absorbent layer structure or core, that contains less than 5%by weight cellulosic fibers.

“Thickness” and “height” are used herein interchangeably.

According to the present invention absorbent material 100 may be fedonto the supporting sheet 16, 16′ by any suitable means includinggravimetric feeding or by using a print roll. In the embodimentillustrated in FIGS. 1A, 1B and 2 the print roll method is used which isdescribed in more detail below.

FIGS. 1A and 1B illustrate examples of patterns which provide areservoir 25 for holding absorbent material prior to depositing, orprinting the absorbent material onto a supporting web. Absorbentmaterial is fed to the reservoir, the reservoir holds absorbent materialin each of the holes or cavities 22. The reservoirs contain one or morechannels 21 between the absorbent regions, the channels 21 beingsubstantially free of absorbent material.

In a preferred embodiment of the invention illustrated in FIGS. 2 and 3the reservoirs are disposed around the outer surface of print rolls 144,156. The absorbent material 100 is delivered to the supporting sheet 16by a roll 156 placed adjacent and in close proximity to the first movingendless surface 30, for example substantially above the surface. Theabsorbent material 100 may be deposited substantially continuously. Thepoint or area where the absorbent material 100 leaves the roll 156 andtransfers to the first moving endless surface 30 is herein referred toas the depositing point or area; and in this point or area a raisedstrip 21, e.g., each raised strip, mates with a mating strip 31, e.g.without direct contact.

A first printing unit 134 for making an absorbent structure inaccordance with the first aspect of this invention is illustrated on theleft half in FIG. 2. A second printing unit 132 for forming a secondabsorbent structure is represented on the right side of FIG. 2, bothabsorbent structures being then combined into an absorbent core in thenip 162.

The first printing unit 134 comprises an auxiliary adhesive applicator148 for applying an auxiliary adhesive to the substrate 16, a firstrotatable support roll 152 for receiving the first substrate 16, a firsthopper 154 for holding the absorbent particulate polymer material, afirst printing roll 156 for transferring the absorbent particulatepolymer material from the hopper 154 to the substrate 16, and athermoplastic adhesive material applicator 158 for applying the fibrousthermoplastic adhesive material 74 to the first substrate 16 and theabsorbent particulate polymer material land areas thereon.

The auxiliary adhesive applicator 148 may be a nozzle system which canprovide a relatively thin but wide curtain of thermoplastic adhesivematerial as suggested in WO 2008/155699, but may instead advantageouslycomprise a slot coater for applying several slots of auxiliary adhesivesimultaneously along the width of the substrate and fitted with amanifold to intermittently stop the delivery of the auxiliary adhesiveso that there the auxiliary layer is not applied in the area of thesubstrate corresponding to the zones of lower absorbent material amount.The printing roll 156 and adhesive applicator 158 may be as furtherdetailed in WO 2008/155699. The absorbent structure 70 obtained by theprinting unit 134 may be directly put in face to face relation with asecond substrate 16′, or may be combined with a second absorbentstructure 70′ to form an absorbent core. This second absorbent structure70′ may be formed on the second printing unit 132 as shown in FIG. 2,which may be generally identical to the first printing unit 134. Thesecond printing unit 132 may comprise a second auxiliary adhesiveapplicator 136 which may be a slot coater for applying an auxiliaryadhesive to the substrate 16′, a second rotatable support roll 140 forreceiving the substrate 16′, a second hopper 142 for holding absorbentparticulate polymer material, a second printing roll 144 fortransferring the absorbent particulate polymer material to the substrate16′, and a thermoplastic adhesive material applicator 146 for applyingthe thermoplastic adhesive material 74′ to the substrate 16′ and theabsorbent particulate polymer land areas thereon.

The radius of the roll 156 may depend on what absorbent structure isproduced, e.g. what size, and for example how many structures areproduced per cycle of the print roll or drum. For example, thedrum/print roll may have a radius of at least 40 mm, or of at least 50mm; it may be for example up to 300 mm, or up to 200 mm. In someembodiments, the radius of the drum/print roll is less than 50% of theradius of the first moving endless surface. In a preferred embodimentthe radius of the print roll is from 60 mm to 80 mm.

The roll 156 may have any suitable width, but for example a width (forexample in CD, hence perpendicular to MD) corresponding (substantially)to the width of the absorbent structure to be produced; this for examplebe at least 40 mm, or at least 60 mm, or for example up to 400 mm, or upto 200 mm.

The roll 156 may have one or more reservoirs 25 with a certain volumefor receiving the absorbent material 100 therein, and transporting it toand then depositing it on the supporting sheet 16 on the first movingendless surface.

Each reservoir 25 corresponds typically to an absorbent structure to beproduced, as suitable for an absorbent article.

According to the present first and second supporting sheets are carriedon first and second moving endless surfaces. In FIGS. 2 to 4 these firstand second moving endless surfaces are illustrated by drums, referred toherein as lay-down drums 140, 152. Alternatively the moving endlesssurfaces could be belts.

The supporting sheets 16, 16′ are preferably sheets of nonwovenmaterial. Absorbent material is deposited onto at least one, andpreferably both, of the supporting sheets from the roll 156, except inthe regions corresponding to the raised strips 21 and the mating strips31.

The first roll 152 has one or more substantially longitudinallyextending first mating strips 31, and the second roll 140 hascorresponding longitudinally extending second mating strips. Pressure isapplied through the first mating strips against an auxiliary bondingroll 160 to the first and second supporting sheets 16, 16′ at leastwithin a part of the area of the channels, so as to adhere together thefirst and second supporting sheets.

By applying pressure to the supporting sheets in this manner, betweenthe first mating strips and the auxiliary bonding roll, rather than byseparate pressure rolls positioned downstream of the rolls, the problemof registration of the channel is avoided. Quality control of theabsorbent structure is more easily provided, especially in high speedmanufacturing processes.

In some embodiments, the first and second moving endless surfaces 140,152 may for example have a speed of at least 1000, or at least 1200parts per minute and/or a linear speed of at least 4.5 m/s, or at least6 m/s, or at least 8 m/s, or at least 10 m/s.

Lay-Down Drum

FIG. 3 illustrates the side-by side arrangement of the print roll 156and the lay-down drum 152. In the embodiment illustrated in FIG. 3 thedrum is a rotating cylindrical drum. The outer shell rotates around astationary inner chamber, e.g. a stator. The rotating outer shellcarries one or more receptacles 33 which receive absorbent material fromthe print roll 156.

Preferably the receptacle 33 is at least partially air-permeable. It mayhave an area that serves to receive the absorbent material, and thisarea is substantially in air-communication with a vacuum system viavacuum chambers 38. This arrangement holds the supporting sheet 16 ontothe surface of the lay-down drum 30, and may also hold the absorbentmaterial received from the print roll 156 in place against the surfaceof the supporting sheet 16, if the supporting web is air permeable.

In one embodiment, not illustrated, the receptacle area 33 other thanthe mating strips 31 is a mesh material that has apertures, is airpermeable, and is in air communication with the chambers 38 of thevacuum system.

In the embodiment of FIG. 3 the surface area of the receptacle 33, otherthan the mating strips 31, comprises thin supports substantially intransverse direction, for supporting the supporting sheet 16. Typicallythe maximum dimension in the longitudinal direction is less than theaverage width dimension of the adjacent mating strip; for example atmost 4 mm, preferably at most 3 mm.

In the embodiment of FIG. 4, the receptacle 33 comprises a multitude ofsubstantially longitudinally extending rods 36, spaced apart from oneanother, and typically from a neighbouring mating strip, in transversedirection. Such rods 36 may then partially form the most outer surfaceof the receptacle 33, so that the supporting sheet 16 is received andcarried by the rods 36 and the mating strips 31.

Pressure is applied between the corresponding first mating strips on thelay-down drum and the auxiliary bonding roll 160 which presses againstthe first and second supporting webs, specifically in the regions inwhich the absorbent structure is free of any absorbent material. Thecombination of pressure and adhesive material between the supportingwebs causes the supporting webs to adhere together in these regions andthus forms one or more channels. The application of pressure can beaccurately registered with the regions which are free of absorbentmaterial because both the deposit of absorbent material and theapplication of pressure take place on the same surface, namely thelay-down drum, receptacle 33. It is preferred to avoid applying anypressure to the absorbent material which is sandwiched between thesupporting webs. Such pressure could cause absorbent material particlesto damage or even puncture or tear the supporting web. Such pressureacting on absorbent material particles between the mating surfaces couldalso cause undue wear to the mating surfaces. For this reason the areaover which pressure is applies between the mating surfaces is preferablyslightly narrower and preferably also slightly shorter than the regionin which the absorbent material is free of any absorbent material.

Preferably the first mating strips 31 are made from a metallic material,preferably steel and the auxiliary bonding roll is made from an elasticmaterial, preferably silicone, or vice versa.

Process Control

In a preferred embodiment the process is controlled in order to maintainthe desired pressure between the mating strips on the lay-down drum andthe corresponding mating strips on the auxiliary bonding roll 160. Theapplied pressure is an important process parameter for achievingrequired channel bond strength in the finished article. In thedescription that follows reference is made to pressure applied betweentwo drums, however the principles may equally be applied to other formsof moving endless surfaces, such as belts, rollers, and combinationsthereof.

Preferably pressure is applied by means of the mating strips which formpart of the outer surface of the drum 30 and the auxiliary bonding roll160. Each drum is mounted on a shaft, and each shaft is rotated at a setspeed by means of a drive, for example an electric motor. Alternativelythe auxiliary bonding roll 160 may be rotated by the contact between thedrum 30. Each shaft is supported in a backplate which, in turn, ismounted directly or indirectly in the machine frame.

According to the preferred bonding system, the drum 30 has a fixed axis,whilst the axis of auxiliary bonding roll moveable, with the axis of thedrum and auxiliary bonding roll staying parallel. Preferably theauxiliary bonding roll is pressed against the surface of the drum with acontrolled force greater than 20N, preferably between 50-3000N.Preferably the applied pressure is controlled pneumatically, byadjusting the distance between the drum and the auxiliary bonding roll,for example by means of cylinder air pressure.

In alternative embodiments the pressure may be applied between twoauxiliary bonding rolls 160, 161, as in FIG. 5B, or by means of two ormore auxiliary bonding rolls 160, as in FIG. 5C, or by means of a belt164, as in FIG. 5D.

The preferred process pressure between the lay-down drum and theauxiliary bonding roll is from 0.3 to 0.8 MPa.

The drums are mounted onto the shaft and the free end of the shaft isreferred to as the outside section of the shaft, whereas the opposingend of the shaft is referred to as the drive-side section of the shaft.

Absorbent Material

The absorbent material 100 herein is preferably a flowable material, inthe dry state, most preferably a particulate material. In particulateform the absorbent material may be particles, flakes, fibers, spheres,agglomerated particles and other forms known in the art.

The absorbent material 100 comprises superabsorbent polymer material,optionally combined with cellulosic material, including for examplecellulose, comminuted wood pulp in the form of fibers. In someembodiments, the absorbent material 100 may comprise at least 60%, or atleast 70% by weight of superabsorbent polymer material, and at the most40% or at the most 30% of cellulosic material. In preferred embodiments,the absorbent layer comprises absorbent material 100 that consistssubstantially of absorbent polymer material, e.g., less than 5% byweight of the absorbent material of cellulosic material is present; andthe absorbent layer/absorbent structure, may be substantially or evencompletely free of cellulosic material.

In preferred embodiments herein, the absorbent material is asuperabsorbent polymer material, herein referred to as SAP, and alsoknown as particulate absorbent gelling material, AGM. The particulateSAP herein may have a high sorption capacity, e.g. having a CRC of forexample at least 20 g/g, or at 30 g/g. Upper limits may for example beup to 150 g/g, or up to 100 g/g.

The particulate SAP may have a good permeability for liquid, forexample, having a SFC value of at least 10×10⁻⁷ cm³ s/g; or preferablyat least 30×10⁻⁷ cm³ s/g, or at least 50×10⁻⁷ cm³ s/g 10×10⁻⁷ cm³ s/g,or possibly permeability SFC value of at least 100×10⁻⁷ cm³ s/g, or atleast a SFC of 120×10⁻⁷ cm³ sec/g. This SFC is a measure of permeabilityand an indication of porosity is provided by the saline flowconductivity of the gel bed as described in U.S. Pat. No. 5,562,646,(Goldman et al.) issued Oct. 8, 1996 (whereby however a 0.9% NaClsolution is used instead of Jayco solution). Upper limits may forexample be up to 350 or up to 250 (×10⁻⁷ cm³ s/g).

In some embodiments herein the polymers of the SAP are internallycross-linked and/or surface crosslinked polymers.

In some embodiments herein, the absorbent material 100 comprising orconsisting of particles of polyacrylic acids/polyacrylate polymers, forexample having a neutralization degree of from 60% to 90%, or about 75%,having for example sodium counter ions, as known in the art; they may besurface crosslinked and/or internally crosslinked polyacrylicacid/polyacrylate polymers.

In some embodiments herein, the absorbent material 100 is in the form ofparticles with, a mass medium particle size up to 2 mm, or between 50microns and 2 mm or to 1 mm, or preferably from 100 or 200 or 300 or 400or 500 μm, or to 1000 or to 800 or to 700 μm; as can for example bemeasured by the method set out in for example EP-A-0691133. In someembodiments of the invention, the material is in the form of particlesof which at least 80% by weight are particles of a size between 50 μmand 1200 μm and having a mass median particle size between any of therange combinations above. The particles may be essentially spherical, ormay have some other shape. Preferably the absorbent material 100 has arelatively narrow range of particle sizes, e.g., with the majority(e.g., at least 80% or preferably at least 90% or even at least 95% byweight) of particles having a particle size between 50 μm and 1000 μm,preferably between 100 μm and 800 μm, and more preferably between 200 μmand 600 μm.

The absorbent material 100 herein may advantageously comprise less than15% by weight of water, or less than 10%, or less than 8% or less than5%. The water-content can be determined by the Edana test, number ERT430.1-99 (February 1999) which involves drying the particulate material100 at 105° Celsius for 3 hours and determining the moisture content bythe weight loss of the particulate material 100 after drying.

The particulate SAP herein may be particles of SAP that are surfacecoated or surface treated (this not including surface-crosslinking,which may be an additional surface-treatment); such coatings and surfacetreatment steps are well known in the art, and include surface treatmentwith one or more inorganic powders, including silicates, phosphates, andcoatings of polymeric material, including elastomeric polymericmaterials, or film-forming polymeric materials.

Supporting Sheet

The absorbent structure produced with the apparatus 1 and method of theinvention comprises a supporting sheet 200, to receive the absorbentmaterial. This supporting sheet 200 may be any individual sheet or websheet material, in particular paper, films, wovens or nonwovens, orlaminate of any of these.

In some embodiments herein, the supporting sheet 200 is a nonwoven,e.g., a nonwoven web, such as a carded nonwoven, spunbond nonwoven ormeltblown nonwoven, and including nonwoven laminates of any of these.

The fibers may be of natural or man-made origin and may be staple orcontinuous filaments or be formed in situ. Commercially available fibershave diameters ranging typically from less than about 0.001 mm to morethan about 0.2 mm and they come in several different forms: short fibers(known as staple, or chopped), continuous single fibers (filaments ormonofilaments), untwisted bundles of continuous filaments (tow), andtwisted bundles of continuous filaments (yarn). The fibers may bebicomponent fibers, for example having a sheet-core arrangement, e.g.,with different polymers forming the sheet and the core. Nonwoven fabricscan be formed by many processes such as meltblowing, spunbonding,solvent spinning, electrospinning, and carding.

The nonwoven herein may be made of hydrophilic fibers; “Hydrophilic”describes fibers or surfaces of fibers, which are wettable by aqueousfluids (e.g., aqueous body fluids) deposited on these fibers.Hydrophilicity and wettability are typically defined in terms of contactangle and the strike through time of the fluids, for example through anonwoven fabric. This is discussed in detail in the American ChemicalSociety publication entitled “Contact angle, wettability and adhesion”,edited by Robert F. Gould (Copyright 1964). A fiber or surface of afiber is said to be wetted by a fluid (i.e., hydrophilic) when eitherthe contact angle between the fluid and the fiber, or its surface, isless than 90°, or when the fluid tends to spread spontaneously acrossthe surface of the fiber, both conditions are normally co-existing.Conversely, a fiber or surface of the fiber is considered to behydrophobic if the contact angle is greater than 90° and the fluid doesnot spread spontaneously across the surface of the fiber.

The supporting sheet 200 herein may be air-permeable. Films usefulherein may therefore comprise micro pores. Nonwovens herein may forexample be air permeable. The supporting sheet 200 may have for examplean air-permeability of from 40 or from 50, to 300 or to 200 m³/(m²×min),as determined by EDANA method 140-1-99 (125 Pa, 38.3 cm²). Thesupporting sheet 200 may alternatively have a lower air-permeability,e.g. being non-air-permeable, to for example be better detained on amoving surface comprising vacuum.

In preferred executions, the supporting sheet 200 is a nonwoven laminatematerial, a nonwoven laminate web, for example of the SMS or SMMS type.

The basis weight of nonwoven fabrics is usually expressed in grams persquare meter (gsm). The supporting sheet 200 may have a basis weightthat is less than 60 gsm, or for example than 50 gsm, for example from 5gsm to 40 gsm, or to 30 gsm.

The supporting sheet 200 may have a transverse-extensibility or alongitudinal-extensibility, for example of more the 20%, or for examplemore than 100%, but for example not more than 200%.

In one of the embodiment herein, the supporting sheet 200 has atransverse dimension that is more than the transverse dimension of thepart of the receptacle (33), e.g. at least 10%, or for example at 20% orat least 30%, and for example up to about 120%.

Adhesive Application Units and Method Steps

The supporting sheet 200 is treated with an adhesive prior to, at,and/or after transfer to the moving endless surface. Thus, the apparatus1 herein comprises adhesive application unit(s) 50, 51. The methodherein also comprises such an adhesive application step.

This adhesive may be applied uniformly and/or continuously, to aidabsorbent material 100 immobilization and then it may help to adhere thesupporting sheet 200 to a further material that may overlay theabsorbent layer, as described below. Alternatively, it may be applied ina pattern. It may be applied by spraying, or for example by selectivelyslot-coating; the apparatus 1 may thus comprise a slot-coater, with apattern.

The adhesive may be applied on those portions of the supporting sheet200 that are to receive to receive the absorbent material; then, ithelps to immobilize the absorbent material 100 thereon (e.g., to ensurethe absorbent material 100 will stay substantially as applied, with thechannels, preferably not only during manufacturing, but also duringstorage and in use (at least during part of the use). Or, alternatively,only on those portions of the supporting sheet 200 that are to be on themating strips 31; then it may help to adhere the supporting sheet 200 toa further material that may overlay the absorbent layer, as describedbelow. It may be applied as substantially longitudinal stripes, forexample.

In some embodiments, the apparatus 1 may comprise a unit to apply anadhesive to the supporting sheet 200 in a pattern, for example thepattern of the mating strips 31, and optionally of the rods 36, ifpresent.

Any suitable adhesive can be used for this, for example so-calledhotmelt adhesives used, for example, sprayable hot melt adhesives, suchas H.B. Fuller Co. (St. Paul, Minn.) Product No. HL-1620-B, can be used.

Alternatively, or in addition, it may be beneficial to apply a furtherimmobilization adhesive to the absorbent structure produced by theapparatus 1 or method herein, e.g. to ensure the absorbent material 100will stay substantially as applied, with the channels, preferably notonly during manufacturing, but also during storage and in use (at leastduring part of the use). This immobilization adhesive may then forexample be applied onto the absorbent layer just after application ofthe absorbent material 100 onto the supporting sheet 200.

The apparatus 1 herein may optionally have a further adhesiveapplication unit 50, e.g., downstream from the absorbent materialdeposition point. The method may have a corresponding method step

This adhesive may be applied uniformly and/or homogeneously. This may bea thermoplastic adhesive material.

In accordance with certain embodiments, the thermoplastic adhesivematerial may comprise, in its entirety, a single thermoplastic polymeror a blend of thermoplastic polymers, having a softening point, asdetermined by the ASTM Method D-36-95 “Ring and Ball”, in the rangebetween 50° C. and 300° C., or alternatively the thermoplastic adhesivematerial may be a hot melt adhesive comprising at least onethermoplastic polymer in combination with other thermoplastic diluentssuch as tackifying resins, plasticizers and additives such asantioxidants. In certain embodiments, the thermoplastic polymer hastypically a molecular weight (Mw) of more than 10,000 and a glasstransition temperature (Tg) usually below room temperature or −6°C.<Tg<16° C. In certain embodiments, typical concentrations of thepolymer in a hot melt are in the range of about 20 to about 40% byweight. In certain embodiments, thermoplastic polymers may be waterinsensitive. Exemplary polymers are (styrenic) block copolymersincluding A-B-A triblock structures, A-B diblock structures and (A-B)nradial block copolymer structures wherein the A blocks arenon-elastomeric polymer blocks, typically comprising polystyrene, andthe B blocks are unsaturated conjugated diene or (partly) hydrogenatedversions of such. The B block is typically isoprene, butadiene,ethylene/butylene (hydrogenated butadiene), ethylene/propylene(hydrogenated isoprene), and mixtures thereof. Other suitablethermoplastic polymers that may be employed are metallocene polyolefins,which are ethylene polymers prepared using single-site or metallocenecatalysts. Therein, at least one comonomer can be polymerized withethylene to make a copolymer, terpolymer or higher order polymer. Alsoapplicable are amorphous polyolefins or amorphous polyalphaolefins(APAO) which are homopolymers, copolymers or terpolymers of C2 to C8alpha olefins. In exemplary embodiments, the tackifying resin hastypically a Mw below 5,000 and a Tg usually above room temperature,typical concentrations of the resin in a hot melt are in the range ofabout 30 to about 60%, and the plasticizer has a low Mw of typicallyless than 1,000 and a Tg below room temperature, with a typicalconcentration of about 0 to about 15%. In certain embodiments, thethermoplastic adhesive material is present in the form of fibers. Insome embodiments, the fibers will have an average thickness of about 1to about 50 micrometers or about 1 to about 35 micrometers and anaverage length of about 5 mm to about 50 mm or about 5 mm to about 30mm.

Test Method

According to the apparatus and method of the present invention, anadhesive bond is formed between first and second supporting sheets in atleast a part of the channel area. The bond strength of the adhesivelyconnected regions may be measured by various test methods. A preferredtest method is the peel strength test method as described in ASTMD-903-98. In case the standard peel rate of 152 mm (6 inches)/minuteresults in the tearing of the fragile supporting sheet, then this ratemay need to be reduced. 10 mm/minute is preferred.

One suitable power-driven machine for use in the test is a verticalsingle column Zwick Tensile Tester Test machine with 50 N force cellwith force accuracy of 0.3% and distance accuracy of 0.15%. The fourfaces of the two jaws should be padded with a thin strip of rubber toprevent slippage as provided by the supplier of the equipment (jaws:Vulkollan glatt 30×60 mm, material number 314366, provider: Zwick GmbH &Co, D-89079 Ulm).

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A method for making an absorbent core, the methodcomprising steps of: rotating a first drum and a second drum in oppositedirections, the first drum positioned proximate the second drum todefine a nip therebetween, the first drum and the second drum eachcomprising a mating strip; advancing a first supporting sheet on therotating first drum; depositing absorbent material on the firstsupporting sheet while advancing on the first drum except in a regioncorresponding to the mating strip to form a first absorbent structurecomprising a channel between absorbent regions, the channel beingsubstantially free of absorbent material; advancing a second supportingsheet on the rotating second drum; depositing absorbent material on thesecond supporting sheet while advancing on the second drum except in aregion corresponding to the mating strip to form a second absorbentstructure comprising a channel between absorbent regions, the channelbeing substantially free of absorbent material; applying adhesive to atleast one of the first supporting and the second supporting sheet;combining the first absorbent structure and the second absorbentstructure at the nip; and bonding the channel of the first absorbentstructure together with the channel of the second absorbent structurewith the adhesive by advancing the combined first and second absorbentstructures between a bonding roll and the mating strip of the firstdrum, wherein pressure is applied to an area of the first and secondabsorbent structures that is narrower and shorter than the channels. 2.The method of claim 1, wherein the absorbent material is a particulatesuperabsorbent polymer material.
 3. The method of claim 1, wherein thestep of applying adhesive is performed prior to the steps of depositingabsorbent material on the first supporting sheet and depositingabsorbent material on the second supporting sheet.
 4. The method ofclaim 1, wherein the step of applying adhesive is performed subsequentto the steps of depositing absorbent material on the first supportingsheet and depositing absorbent material on the second supporting sheet.5. The method of claim 1, wherein the mating strips of the first andsecond drums are made from steel.
 6. The method of claim 1, wherein themating strips of the first and second drums are made from silicone. 7.The method of claim 1, wherein the drum comprises an outer shell thatcomprises an air permeable receptacle for receiving the first supportingsheet thereon, and wherein the outer shell is connected to a vacuumsystem for facilitating retention of the first supporting sheet and theabsorbent material thereon.
 8. The method of claim 7, wherein thereceptacle further comprises a multitude of substantially longitudinallyextending rods, spaced apart from one another in a transverse direction,each rod having a maximum width dimension of at least about 0.3 mm andless than about 2.5 mm, the rods each having an average height dimensionof at least about 1 mm.
 9. The method of claim 1, wherein the step ofdepositing absorbent material on the first supporting sheet furthercomprises transferring the absorbent material from a feeder comprising areservoir formed by a plurality of cavities.
 10. A method for making anabsorbent core, the method comprising steps of: rotating a first drumand a second drum in opposite directions, the first drum positionedproximate the second drum to define a nip therebetween, the first drumand the second drum each comprising a mating strip; advancing a firstsupporting sheet on the rotating first drum; depositing absorbentmaterial on the first supporting sheet while advancing on the first drumexcept in a region corresponding to the mating strip to form anabsorbent structure comprising a channel between absorbent regions, thechannel being substantially free of absorbent material; advancing asecond supporting sheet on the rotating second drum; applying adhesiveto at least one of the first supporting and the second supporting sheet;combining the absorbent structure and the supporting sheet at the nip;and bonding the channel of the absorbent structure together with thesecond supporting sheet with the adhesive by advancing the combinedabsorbent structure and second supporting sheet between a bonding rolland the mating strip of the first drum or the second drum, whereinpressure is applied to an area of the first supporting sheet and thesecond supporting sheet that is narrower and shorter than the channels.11. The method of claim 10, wherein the absorbent material is aparticulate superabsorbent polymer material.
 12. The method of claim 10,wherein the step of applying adhesive is performed prior to the step ofdepositing absorbent material on the first supporting sheet.
 13. Themethod of claim 10, wherein the step of applying adhesive is performedsubsequent to the step of depositing absorbent material on the firstsupporting sheet.
 14. The method of claim 10, wherein the mating stripsof the first and second drums are made from steel.
 15. The method ofclaim 10, wherein the mating strips of the first and second drums aremade from silicone.
 16. A method for making an absorbent core, themethod comprising steps of: rotating a first drum and a second drum inopposite directions, the first drum positioned proximate the second drumto define a nip therebetween, the first drum and the second drum eachcomprising a mating strip; advancing a first supporting sheet on therotating first drum; depositing absorbent material on the firstsupporting sheet while advancing on the first drum except in a regioncorresponding to the mating strip to form a first absorbent structurecomprising a channel between absorbent regions, the channel beingsubstantially free of absorbent material; advancing a second supportingsheet on the rotating second drum; depositing absorbent material on thesecond supporting sheet while advancing on the second drum except in aregion corresponding to the mating strip to form a second absorbentstructure comprising a channel between absorbent regions, the channelbeing substantially free of absorbent material; applying adhesive to atleast one of the first supporting and the second supporting sheet;combining the first absorbent structure and the second absorbentstructure at the nip; and bonding the channel of the first absorbentstructure together with the channel of the second absorbent structurewith the adhesive by advancing the combined first and second absorbentstructures between the mating strip of the first drum and a plurality ofbonding rolls or a belt.
 17. The method of claim 16, wherein theabsorbent material is a particulate superabsorbent polymer material. 18.The method of claim 16, wherein the step of applying adhesive isperformed prior to the step of depositing absorbent material on thefirst supporting sheet.
 19. The method of claim 16, wherein the step ofapplying adhesive is performed subsequent to the step of depositingabsorbent material on the first supporting sheet.
 20. The method ofclaim 16, wherein the mating strips of the first and second drums aremade from silicone.